Leakage Pathways Research Articles

Nano Sealant for CO2 Seal Integrity and Overcoring at Mont Terri

Wellbore integrity is an important consideration for the viability of subsurface CO2 sequestration. Wellbores may leak due to micro annuli that develop between annular cement and steel casing and/or the host formation, as well as fractures and flaws in the cement itself. Leakage pathways may be problematic for the long-term containment of CO2. To address the need for a repair material that can effectively seal and repair wellbores, a new nanotechnology-based sealant has been developed at the University of New Mexico, USA. The sealant, referred to TS-Nano 20™, has superior flowability, excellent bond strength to steel and rock, is very ductile, and is thermally stable. Moreover, the sealant has been demonstrated to readily flow into microcracks below 20 µm under modest pressure gradients. The sealant showed excellent bond strength and superior fatigue resistance to debonding under stress cycles than microfine cement and other sealants. TS-Nano 20™ was used in a field test at the Mont Terri Underground Research Laboratory (MT-URL) located in NW Switzerland. This experimental work at MT-URL was performed under the auspices of the CO2 Capture Project (CCP), a three-company collaboration comprising Chevron, BP, and Petrobras. The CCP effort is directed to develop more cost-effective and efficient processes for CO2 concentration, capture and sequestration applied to the energy, refining, chemical, and power generation industries in order to reduce greenhouse gas emissions. A wellbore with a cemented annulus was located beneath the floor of the underground laboratory. The wellbore was intentionally damaged by thermal cycling inside the casing to produce leakage pathways in the wellbore system. The wellbore system included injection ports at several locations along its length to allow pressure and flow tests to be conducted to document the leakage along the length of the wellbore system. Subsequently, various sealants were injected into the injection ports to seal the leakage pathways within the wellbore system. The sealant was then successfully injected into two of the intervals on site. After injection of sealants, the entire wellbore system needed to be stabilized for eventual overcoring and forensic analyses. To this end, a large open hole test interval (uncemented) at the bottom of the wellbore was first filled with a very flowable cement slurry to chase out water and reduce the dead volume, and then the sealant was injected on top of the cement and squeezed into leakage pathways that remained near the bottom of the wellbore system and cracks in the clay formation. Additionally, the sealant was used to further stabilize portions of the wellbore by injecting into all the previously used injection ports. We report on the ability of the nano sealant to maintain its flowability and mechanical characteristics under relatively low temperature and meet all field injection requirements, including having a relatively long-time to gel while hardening after injection. Pressure and permeability measurements from the field tests are reported documenting the ability of the sealant to seal relatively very thin microcracks and create appropriate conditions for overcoring.

Multi-Scale Investigation of Caprock-Cement Integrity for CO2 Storage

CO2 storage in saline aquifers and depleted oil and gas reservoirs is a promising solution to help mitigating CO2 emissions and tackling global warming. However, storage security and CO2 leakage over a long period remain as a major concern. Cement degradation after CO2 injection, especially in poorly cemented wells, can provide pathways for CO2 leakage to groundwater and the atmosphere. Therefore, to assess the potential risks of CO2 leakage, it is critical to understand the interactions between the major components of a storage system including CO2, brine, wellbore cement, and caprock/reservoir rocks. In this work, we performed a series of experiments simulating deep wellbore environments to investigate the chemical, physical, and mechanical alterations in cement and rock as a result of being exposed to CO2-rich brine. X-ray micro-computer tomography (µCT), petrophysical evaluation and geomechanical testing were conducted before and after experiments. It was observed that dissolution and precipitation of some minerals started from early stage of exposure and continued as time passed, and, as a result, cement and cement-caprock interface were affected. The high-permeable hairline cracks in the cement were filled due to mineral precipitation and reduced the composite permeability significantly. This phenomenon may help mitigate against CO2 leakage at conditions similar to those used in this work.

Flow modelling to quantify structural control on CO 2 migration and containment, CCS South West Hub, Australia

In order to reduce uncertainties around CO 2 containment for the South West Hub CCS site (Western Australia), conceptual fault hydrodynamic models were defined and numerical simulations were carried out. These simulations model worst-case scenarios with a plume reaching a main compartment-bounding fault near the proposed injection depth and at the faulted interface between the primary and secondary containment interval. The conceptual models incorporate host-rock and fault properties accounting for fault-zone lithology, cementation and cataclastic processes but with no account made for geomechanical processes as the risk of reactivation is perceived as low. Flow simulations were performed to assess cross-fault and upfault migration in the case of plume–faults interaction. Results near the injection depth suggest that the main faults are likely to experience a significant reduction in transmissivity and impede CO 2 flow. This could promote the migration of CO 2 vertically or along the stratigraphic dip. Results near the interface between the primary and secondary containment intervals show that none of the main faults would critically control CO 2 flow nor would they act as primary leakage pathways. CO 2 flow is predicted to be primarily controlled by the sedimentological morphology. The presence of baffles in the secondary containment interval is expected to be associated with local CO 2 accumulations; additional permeability impacts introduced by faults are minor. Thematic collection: This article is part of the Geoscience for CO 2 storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage

Integrated Testing of Building Fabric Thermal Performance for Calibration of Energy Models of Three Low-Energy Dwellings in the UK

This paper presents the methodology and results of in situ testing of building fabric thermal performance to calibrate as-built energy models of three low-energy dwellings in the UK, so as to examine the gap between as-designed and as-built energy performance. The in situ tests included repeat testing of air permeability (AP) integrated with thermal imaging survey and heat flux measurements of the building fabric elements, along with concurrent monitoring of indoor temperature during the pre-occupancy stage. Despite being designed to high thermal standards, wall and roof U-values were measured to be higher than expected. Thermal imaging surveys revealed air leakage pathways around door/window openings, penetrations and junctions between walls and ceilings, indicating poor detailing and workmanship. AP was found to have increased after the initial test due to post-completion alteration to the building fabric. Though the results did not meet design expectation, they were within the UK Building Regulations. Calibration of energy models with temperature monitoring provided a less extreme energy performance gap than simply replacing the designed values with test results. Insights from this study have reinforced the need for building regulations to require integrated testing of building fabric as part of housing delivery to ensure performance targets are realised.

Establishment of analysis methodology of RADTRAD for Maanshan PWR ATWS

Abstract In this research, the analysis methodology for Maanshan PWR nuclear power plant (NPP) ATWS (Anticipated Transient Without Scram) is established by using RADTRAD code. This methodology can evaluate the dose at Exclusion Area Boundary (EAB), Low Population Zone (LPZ), and control room for the Maanshan ATWS. In addition, there are four leakage pathways in the Maanshan ATWS that are containment leakage, containment low volume purge, steam generator leakage, and ESF leakage. Therefore, for these leakage pathways, the RADTRAD models are established. Finally, according to the analysis results, they are below the criteria of 10 CFR 100.11 for the EAB and LPZ and Standard Review Plan (SRP) for the control room. Additionally, the steam generator leakage gives the maximum dose in these leakage pathways.

Assessment of Trans-Boundary Effects at LBr-1 CO2 Storage Pilot Site and Regulatory Solutions

The paper evaluates possible trans-boundary issues related to planned CO2 injection and storage at LBr-1, a candidate structure for a future geological storage pilot. LBr-1 is an abandoned hydrocarbon field situated in the Czech part of the Vienna Basin, close to the Czech-Slovak border. At first, currently valid national legislations relevant to CO2 geological storage in the Czech Republic and Slovakia were examined. In the second step, implications of the current legislation and regulatory regimes on the LBr-1 site itself were studied. The most important finding is that both the storage site and storage complex are located entirely on the territory of the Czech Republic. However, several trans-boundary issues were identified, especially those that are related to possible (even if unlikely) leakage of CO2 from the storage complex. Four possible types of trans-boundary issues were examined in detail – pressure build-up, possible leakage through boreholes, possible leakage through faults and possible migration of fluids out of the reservoir due to exceeding spill points for three scenarios – limited CO2 storage, full storage and CO2-EOR scenario. While pressure build-up and leakage through faults do not appear to cause trans-boundary issues, the other two phenomena need to be carefully considered. In case CO2 leakage appears either through abandoned wells or due to exceeding the southern spill point, the analysis of possible leakage pathways shows that the CO2 could migrate into the territory of Slovakia. These findings mean that a cooperation of regulatory authorities from both Czech and Slovak Republics will be necessary to prepare and operate the storage site. This is a significant complicating factor for possible injection of CO2 at LBr-1. Despite of this, the realization of a CO2 storage project on the site is considered viable, especially in the basic pilot storage scenario. This case avoids the spill-point related concerns (because of the limited extent of CO2 plume) and involves only a limited number of abandoned wells that need to be taken care of concerning their abandonment status.

An application of electrical resistivity tomography to investigate leakage pathways in the exploitation of IREO

For the mining of ionic rare earth ore (IREO) by in-situ leaching, the fracture structure, underground river and karst cave developed beneath the ore body, will become leakage pathways for the leaching liquors to escape and seriously reduce the recovery rate of IREO, in addition, the leach liquor along leakage pathways will also cause environmental pollution. Therefore, it is of great significance to study the deep structures and identify the leakage pathways. Our study area situates in Chang Ting county of Fujian province, which is an important rare earth deposit of China, in order to obtain high resolution deep electrical model, the electrical resistivity tomography based on multi-electrode resistivity method was used in this paper. First, we carried out multi-electrode resistivity method parameter experiment and select appropriate exploration parameters; Then, the Multi-electrode resistivity method data acquisition of 11 lines is completed by using ws-2 device mode; After that, the deep electrical structure model of the study area is obtained by inversion calculation and the thickness of the granite weathering layer (the layer containing rare earth ore) and the spatial distribution characteristics of the deep fracture structure are delineated by the deep electrical structure model of the study area. The interpretation results are consistent with the drilling results laid out in the study area. The exploration results provide important reference for the reserve evaluation of ion type rare earth mine, the sealing of leakage pathways and the layout of recovery pathways.

Demonstration of highly repeatable room temperature negative differential resistance in large area AlN/GaN double-barrier resonant tunneling diodes

Here, we present a systematical investigation of AlN/GaN double-barrier resonant tunneling diodes (RTDs) grown by plasma-assisted molecular beam epitaxy on metal-organic chemical vapor deposition GaN-on-sapphire templates. The processed devices featured an active region composed of 2.5 nm GaN quantum well sandwiched by two 1.5 nm AlN barriers and RTD mesa diameter ranging from 1 to 20 μm. Room temperature current–voltage characteristics exhibited a repeatable negative differential resistance (NDR) free of degradation and hysteresis after 1000 times subsequently up-to-down voltage sweeps across different sizes. High peak-to-valley current ratios of 1.93 and 1.58 were obtained at room temperature for 1 and 12 μm diameter devices, respectively, along with peak current densities of 48 and 36 kA/cm2 corresponding to peak voltages of 4.65 and 5.9 V. The peak current density decreased quickly initially and then was less susceptible to this averaging effect with increasing the device diameter. Temperature-dependent measurements revealed that the valley current density displayed a positive relationship to the temperature, and an abruptly increasement was observed for the devices with a diameter of 20 μm when the temperature rose over 230 K. We attributed this abnormal phenomenon to the increased contribution from acoustic and longitudinal optical (LO) phonon scattering, especially for the LO phonon scattering. The area dependence of electrical performance suggested that the leakage pathway through dislocations played a vital role for charge transport and there existed a threshold of dislocation density for NDR characteristics. These results promote further study for future implementation of III-nitride-based RTD oscillators into high-frequency and high-power terahertz radiation.

Comparison of the penetration depth of five root canal sealers: A confocal laser scanning microscopic study.

Background:Sealer penetration into dentinal tubules eliminates the pathways for bacterial leakage and entombs intratubular bacteria.Aim:The aim of this study was to evaluate and compare the depth of radicular dentinal tubule penetration of five root canal sealers using confocal laser scanning microscopy.Methods:Fifty freshly extracted single-rooted maxillary anterior teeth were used. After decoronation at the cementoenamel junction, they were prepared to ProTaper size F3. After irrigation with 5 mL smear clear, 5 mL 5% sodium hypochlorite and 5 mL distilled water alternatively, the samples were randomly divided into five groups (n = 10) and obturated by lateral compaction technique using the test sealers labeled by fluorescent rhodamine B dye (Mayor Diagnostics, Mumbai, India). Zinc oxide eugenol (ZOE) (Prime Dental Products), EndoREZ (Ultradent), Sealapex (SybronEndo), AH Plus (Dentsply Maillefer), and MTA-Fillapex (Angelus) formed the test groups. Teeth were then positioned in blocks of orthodontic resin. Three horizontal sections of 1-mm representing coronal middle and apical thirds were made and examined with Zeiss (laser scanning microscope [LSM] 780) confocal LSM. Images were analyzed using ZEN 2.1 software.Statistical Analysis:Data were recorded and subjected to statistical analysis using one-way ANOVA test.Results:Maximum penetration depth was demonstrated by AH Plus in the coronal and apical thirds, MTA-Fillapex in the middle thirds, while minimum penetration depth was seen in ZOE in the coronal and middle thirds and Sealapex in the apical thirds. None of the root canal sealers were able to penetrate the complete depth of radicular dentinal tubules.Conclusion:While AH Plus and MTA-Fillapex showed the highest penetration into radicular dentinal tubules, ZOE and Sealapex demonstrated the least penetration.

Evaluation of Relationship Between Post-injection Plume Stability and Leakage Risks

One of the critical questions for geologic CO2 storage is how long should a storage site be monitored after the injection is stopped. A storage site operator is required to demonstrate that the storage site is evolving towards long-term stability and the injected CO2 as well as reservoir pressure do not pose any threat including to the groundwater. Migration and evolution of injected CO2 plume depend on site-specific geologic structure, storage reservoir properties as well as operational conditions. While injected CO2 plume may continue to evolve after injection is stopped, its dynamic evolution does not directly imply imminent leakage risk. Leakage risks depend on multiple factors including not only CO2 presence but also reservoir pressure and the characteristics of potential leakage pathways. We performed a modeling based study to evaluate the relationship between post-injection plume migration and leakage risks. Our hypothetical case study is based on the Rock Springs Uplift in southwestern Wyoming in USA. We used a numerical model to perform multiple sets of reservoir simulations each with 29 equi-probable realizations of reservoir permeability heterogeneity, simulating different injection scenarios. We applied newly developed moment-based plume mobility metrics to characterize the migration and evolution of injected CO2 plume. The plume mobility metrics provided detailed analyses of the effect of reservoir permeability heterogeneity and CO2 injection rate on spatial and dynamic evolution of CO2 and overpressure plume. Next, we assessed the potential leakage risks using the integrated assessment modelling approach developed by US DOE’s National Risk Assessment Partnership (NRAP). The combined leakage risk assessment and plume mobility analyses results indicate that lack of CO2 plume stability (or non-zero plume mobility) may not directly imply groundwater aquifer endangerment and the leakage risks are dependent on multiple factors, including presence of wells and their locations and types. This paper is a condensed version of a peer-reviewed paper by Pawar et al [1] published in the International Journal of Greenhouse Gas Control.

Integrated Laboratory and Numerical Investigation of Leakage Pathways Development in CO2 Injection Wells

The integrity of the cement sheath is the crucial part to maintain zonal isolation and to prevent the unwanted leakage of injection fluid for CO2 injection wells. During the lifespan of an injection well, loads arising from multiple processes can affect the state of stress in the wellbore system and, under severe conditions, may induce failure in the cement sheath. Different types of failure, including debonding (micro-annuli), radial cracking, and shear failure, can occur throughout the life of the well and cause severe leakage problems and dramatically reduces the injection efficiency. The MT-URL Well-Sealing experiment is designed to test the efficacy of novel sealants in a well with induced defects via pressure and thermal cycling (pressure and heating tests) as a proxy field scaled well that has undergone damage during CO2 injection. The MT-URL well is highly instrumented and has proven can closely mimic complex cased and cemented interval delaminations (debonding) at the casing-cement and cement-formation boundaries as well as fracturing within the cement sheath. The MT-URL is located in NE Switzerland near the village of St. Ursanne (Fig. 1). This study uses the integrated staged finite element and the laboratory bench-scaled measurement approach to simulate loads arising during the lifespan of the Mt. Terri CO2 injection well and to predict the initiation, evolution, and severity of cement failure under downhole conditions. Particular emphasis is placed on the cement hardening process due to its significant influence on the failure occurrence in the cement. To obtain the temporal variation of cement material properties for subsequent numerical simulation, an experimental procedure, including the measurement of elastic parameters and bleeding test for cement fluid loss, is performed under downhole conditions of the Mt. Terri CO2 injection well. The staged finite element approach used to simulate the cement hardening process in this study includes major processes that have significant mechanical influences, such as the development of elastic properties, bulk shrinkage, reduction of pore pressure, and development of strength. The resulting state of stress is analyzed to assess the onset and evolution of cement failure in the composite wellbore system under downhole conditions. The knowledge from this study can raise awareness of the necessity of predicting and evaluating cement failure and wellbore integrity under downhole conditions. The enhanced understanding of the cement hardening process and cement failure occurrence can provide insights and guidance to future construction of CO2 injection wells and optimize the operation process of CO2 injection.

Potential CO2 leakage from geological storage sites: advances and challenges

This paper provides an overview of recent advances and remaining challenges in predicting, quantifying, detecting and mitigating carbon dioxide (CO2) leakage from geological storage sites to overlying aquifers and the atmosphere. Sequestering carbon dioxide in deep geological formations offers a promising solution for reducing anthropogenic carbon dioxide emissions. However, there remain critical questions regarding the storage integrity and leakage potential, which warrant further consideration. Leaking carbon dioxide out of the reservoir may affect the shallower subsurface – for example, the quality of drinking groundwater, which causes great health risk and public concern. In addition, high concentrations of carbon dioxide in soil would be fatal for vegetation near the surface. Trapping mechanisms and potential leakage pathways are discussed. A detailed review of monitoring methods including atmospheric monitoring, near-surface and subsurface monitoring methods are presented and discussed. In addition, recent numerical and analytical models for predicting the behaviour of carbon dioxide plume and leakage potential are discussed. Despite various research efforts and significant advances made on different aspects of this issue, further investigation is required to ensure safe and effective implementation of large-scale carbon dioxide sequestration projects.

CO2‐water‐rock interactions in undeformed and sheared claystone caprocks from Northern Europe

AbstractOne of the most promising, cost‐effective, and readily available technologies for reducing greenhouse gas emissions to the atmosphere is the capture and separation of CO2 from large stationary sources and storage in geological formations. Storage security, especially in the early stages of operation, is mostly guaranteed by caprock formations with very low permeability overlying the reservoir, capable of containing the injected fluid. Chemical alterations of the formation brine, caused by CO2 injection may cause dissolution and precipitation of secondary minerals, potentially increasing the risks of leakage from the reservoir. In order to evaluate these processes and their potential to induce the formation of leakage pathways in ultrafine fault gouges, a series of batch experiments was performed on crushed and sheared samples from three different caprock formations from Northern Europe (Sollingen, Röt and Opalinus claystones). The experiments were supported by numerical models of the kinetics of mineral dissolution and precipitation simulating the same experimental conditions, and over a longer time (10 000 years). Minor mineral alterations were observed after the batch experiments, the most important being: illite dissolution for the Opalinus and Röt formation samples, and dolomite dissolution and the transformation of illite and chlorite into kaolinite for the Sollingen sample. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Geochemical and geoelectrical characterization of the Terre Calde di Medolla (Emilia-Romagna, northern Italy) and relations with 2012 seismic sequence

Soil gas and Electrical Resistivity Tomography (ERT) surveys were performed in Medolla (Emilia-Romagna Region, northern Italy) within a farming area characterized by macroseeps, absence of vegetation and anomalous temperatures of soil to investigate the soil gas migration mechanism and verify the presence of a buried fault intersecting the macroseeps. Soil gas (222Rn, 220Rn, He and C2H6) concentrations and flux (φCO2 and φCH4) measurements were carried out from 2008 to 2015, comprising the 2012 Emilia seismic sequence. Moreover, in 2016 a ERT survey, combined with new flux measurements, was performed along four profiles (ranging from 180 to 630 m long) centered on the main macroseep.We found that the seismic sequence sensibly influenced the soil gas distribution in the area. All investigated species, but He, increased their values early after the mainshocks, likely due to crustal deformation which promoted the geogas uprising. In 2015, when the stress has vanished, these concentrations gradually decreased toward pre-seismic values.Helium concentrations showed an opposite behavior as they decreased in May 2012 and then gradually increased over time. This trend may be reasonably due to the enhancement of the strain field which promoted the He dissipation from soil to the atmosphere, due to its high volatility.In all the geochemical surveys conducted from 2008 to 2015, soil gas high values around the main macroseeps were identified, delighting the presence of an alignment in the E-W direction. This trend, identified for several gas species, ultimately supports the theory of a hidden fault which favors the intensification of fluids migration along zones characterized by greater permeability.ERT results highlighted a sub-horizontal layering characterized by different resistivity intervals, roughly matching local stratigraphy. In most profiles we observed a slightly increase of resistivity and a sharp interruption of the electro-layering in correspondence of the main macroseep, both near the surface and at depth. This implies that a fracture zone due to the presence of a buried fault cannot be excluded.The combined use of geochemical and geophysical techniques in this study confirmed the usefulness of such multiparametric approach for mapping out hidden structures in tectonically active areas, allowing to better understanding the fluid migration processes through preferential leakage pathways.

Characterization of the Microstructure of the Cement/Casing Interface Using ESEM and Micro-CT Scan Techniques

Summary Integrity of the cement/casing interface is an essential element of establishing an effective barrier system in cased and cemented wellbores. Failure to establish and maintain an effective barrier can result in negative environmental and economic impacts, such as leakage of formation fluids into the environment or loss of production and costly remediation. The main focus of this paper is defined as the characterization of the cement/casing interface microstructure, which is critical for better understanding of the requirements for establishing effective zonal isolation and the long-term integrity of cemented wellbore sections of active wells, as well as the integrity of the abandoned wells. The primary objectives of this study were: first, to confirm the most suitable methods for preparing cement/casing samples and characterize the microstructure of the cement/casing interface (i.e., quantify the size of the microchannel due to possible debonding (gap) at the cement/casing interface and its progression along the wellbore axis); and second, to understand how different test methods can affect the microstructure, and once we have a firm baseline, analyze the effect of different cement compositions on the performance. More specifically, we have investigated effects of the cement composition and preparation, environmental conditions [i.e., relative humidity (RH) of the storage and testing conditions], cement shrinkage, and the expansion additive on the integrity of the cement/casing interface at the micrometer scale by using environmental scanning electron microscope (ESEM, 0.05 µm resolution) and microcomputed tomography (μ-CT, 11.92 µm resolution) scanning techniques. Cemented casing samples were prepared by using Class G and special abandonment cement blends with and without expansion additives and stainless-steel pipes. Results showed that any significant change in the RH of the environment during the cement preparation, curing, and testing process significantly affects the size of the gap at the cement/casing interface in test samples. Analyses of the ESEM images have shown that the 2D nonuniform gap size between the cement and the casing is inversely proportional to the change in the RH of the environment. Results suggested that cement slurries set and cured under downhole conditions with relatively constant RH may not undergo significant shrinkage and yield only minimal debonding effect. The 3D gap model reconstructed from the µ-CT images confirmed that the gap between cement and casing mostly occurred at the cement polished surface and the gap didn’t show any significant connectivity below the cement polished surface, indicating that common sample preparation methods can significantly affect the near-surface interface. Cement blends prepared with expansion additives have shown smaller gap size. The use of expansion additives enhances the cement/casing interface integrity by effectively reducing the gap size at the cement/casing interface. We conclude that as long as the RH of the environment does not change significantly, the cement is expected to undergo a limited shrinkage, and the gap between the cement and the casing may not induce any significant leakage pathway because the gap is only locally distributed at the cement polished surface without showing any significant connectivity along the wellbore axis.

Insights from in-situ measurement of building fabric thermal performance of three zero energy dwellings in UK

In-situ testing of actual building performance is vital to achieve the UN Sustainable Development Goal 11 (Sustainable cities and communities) in reality, given the growing concern that low energy dwellings often underperform against design specifications. This paper presents the methodology and results of in-situ measurements of the building fabric thermal performance of three zero energy dwellings in the UK, using blower door test (air permeability), heat flux measurement (thermal transmittance/U-value) and thermal imaging survey (heat losses). Despite being designed to high thermal standards, air permeability tests showed that none of dwellings met the design air permeability target, with actual results of 5.4 – 7.5 m3/h/m2@50Pa. Air permeability was found to have increased after the initial test due to post-completion alteration to the fabric, although it remained within the UK Building Regulations requirements. Heat flux measurements showed poor thermal quality of the walls and roof section even for the ‘good’ sections that were measured. Thermal imaging surveys revealed where fabric performance was being compromised. Air leakage pathways were found around door/window openings, penetrations and junctions between walls and ceilings indicating poor workmanship. Insights from this study have reinforced the need to have updated as-built energy models with in-situ performance data to reduce performance gap.

Coupled hydro-chemo-mechanical model for fault activation under reactive fluid injection

Pre-existing faults cross-cutting caprock formations constitute potential leakage pathways during geological CO2 sequestration. When the fault filling material is calcite-rich, dissolution of the fault minerals is expected to occur causing the mechanical weakening of the fault or, even worse, its reactivation. In turn, these chemical-mechanical processes influence the distribution of pore pressure in the vicinity of the fault. Hence, a fully coupled approach including the chemically-induced alteration is necessary while investigating fault’s mechanical stability. In this paper, we present a simplified set of equations that allows the resolution of the coupled hydro-chemo-mechanical problem of reactive fluid flow inside a fault. Empirical relationships are used to describe the change of the fault’s material mechanical properties with porosity. The derived model was used to simulate the evolution of the hydro-chemo-mechanical behavior of a fault following an expected leakage scenario during CO2 storage in the Dogger formation in the Paris Basin. The simulation results showed that under normal conditions, fault reactivation is unlikely to happen even in the long term (∼100 years). Nevertheless, the proposed model is capable of capturing the evolution of fault reactivation and has the potential to become a useful element of the toolbox for assessing the risks related to fault reactivation and leakage for CO2 storage projects.

A methodology for reactive transport modelling and geomechanical investigation of wellbores in CO2 storage sites

The movement of injected CO2 from injection wells in CO2 storage sites creates an acidic environment that comes into contact with the cement sheath with a possible consequential effect on its sealing performance. Thus the durability of the cement sheath can be threatened due to the degradation process and the stress state resulting from the new conditions found underground. The integrity of the cement sheath is a function of the cement composition, surrounding rock type, fluid pressure, stress state, temperature, and the type of well. This paper provides a methodology to investigate the stability of the rock-cement-casing assemblage. The assemblage’s mechanical behaviour is coupled with the chemical alterations resulting from it being in contact with CO2-bearing fluids. The cement matrix is a quasi-brittle material which shows a plastic behaviour. The character of the geomechanical part and the geochemical aspect mutually affects each other which is studied in this paper. A plastic-damage approach benefiting from the concept of embedded bands is also introduced to characterise the performance of the cement sheath within CO2 storage sites. This approach considers both the failure and the deformation phenomena occurring within altered zones. In this paper, injection and abandoned wells are hypothesised at depths between 800 and 2500 m and their performance investigated. It is shown that abandoned wells are considered more likely to remain safe while the interfacial transition zones in injection wells are predicted to fail, which converts them to potential leakage pathways. Nevertheless, caution should be taken when the real wells are considered to match the required assumptions in the Introduction Section. In injection wells at depths of 1225–2500 m the cement-casing interface encounters pure dilation. However, the compaction process deforms the rock-cement interface at depths of 800–2500 m, which increases its durability again.

Parametric study on the integrity of wellbores in CO2 storage sites

Carbon capture and storage is considered as an amelioration technique to address the increasing level of carbon dioxide in the atmosphere. Depleted oil and gas reservoirs are potential candidates for the long sequestration of the captured carbon dioxide. The huge number of drilled oil and gas wells in these hydrocarbon reservoirs around the world, however, pose a threat to the integrity of geological CO2 storage projects. These wells are direct connections to the Earth’s surface and even when capped, any defects in their structure can become high leakage pathways. To predict the consequences of this possible loss, a model was developed and introduced by the authors based on coupling the geochemical and geomechanical alterations benefitting from a plastic-damage model. This model simulates the alteration of the rock-cement-casing assemblage in abandoned wells for carbon storage sites. In this paper, a parametric study has been established to investigate the wellbore integrity at various conditions found underground. The results show that separation at the cement-casing interfaces is highly probable in injection wells. The abandoned wells will maintain their integrity within the first thousand years after exposure to CO2-bearing fluids. Our observations suggest that the compaction of the cement-rock interfacial transition zone helps the cement sheath maintain its integrity for a longer period of time.

Grain Boundary Defect Passivation of Triple Cation Mixed Halide Perovskite with Hydrazine-Based Aromatic Iodide for Efficiency Improvement

Perovskites have been unprecedented with relatively sharp rise in power conversion efficiency in the last decade. However, the polycrystalline nature of the perovskite film makes it susceptible to surface and grain boundary defects, which significantly impedes its potential performance. Passivation of these defects has been an effective approach to further improve photovoltaic performance of the perovskite solar cells. Here, we report use of a novel hydrazine-based aromatic iodide salt or phenyl hydrazinium iodide (PHI) for secondary post treatment to passivate surface and grain boundary defects in triple cation mixed halide perovskite films. In particular, the PHI post-treatment reduced current at the grain boundaries, facilitated an electron barrier and reduced trap state density, indicating suppression of leakage pathways and charge recombination, thus passivating the grain boundaries. As a result, a significant enhancement in power conversion efficiency to 20.6% was obtained for the PHI-treated perovskite device in comparison to control device with 17.4%.